This invention relates to a location system and, in particular, to a system which can be used to support personalisation and mobility in typical office environments and in particular to systems of the type disclosed in our British Patent Application No. GB-A-2320089.
It is desirable in a system such as a computer network to have information about location of all the equipment attached to the network and also information about the locations of people using the network and their particular needs at any given time. Usually, the people using the network are mobile but the equipment S fixed. However, in systems such as radio networks, portable equipment can be part of the network and communicates with the network by radio, and even in wired networks equipment can usually be moved around or rotated.
Location systems give absolute information about the locations of objects in space. Typically, the users of information systems are interested in relative location information. This must be derived from the absolute information about objects and persons in space which is the primary data generated by a location system. For example, the sentences xe2x80x9cthe person is at position pxe2x80x9d and xe2x80x9cthe workstation is at position q, facing in direction dxe2x80x9d give absolute location information. However, xe2x80x9cthe person at position p is able to use the workstation at position qxe2x80x9d gives relative location information. In order to make a location system valuable to the users of information systems such as computer networks, a method of deriving relative location information from absolute location information is required.
A preferred embodiment of the present invention enables relative Location information to be derived from absolute location information by expressing the relative location information in terms of spatial containment and overlapping relationships. These can be calculated using absolute location information. For example, to determine the truth of the sentence xe2x80x9cthe workstation can be used by the personxe2x80x9d, a shape c is used to represent the area of space in which the workstation can be used, and another shape p to represent the person. We can then say that the workstation can be used by the person if, and only if, the space c contains the space p. By using this absolute location information to fix the locations of c and p, the truth value of the relative location sentence can then be determined.
In practice, it is necessary to monitor movements of people and objects so that the system can be notified whenever some relative location information becomes true or false. For example, it is necessary to be notified whenever the person p moves into or out of the space in which he can use the workstation c. If there were, for example, 1000 objects such as workstations attached to a network, each of which has an associated area of space, whenever a person moves there are potentially 1000 relative Location statements which could become true or false. To evaluate the truth values of all these statements by calculating the associated containment relationships each time a person or object moves would be too expensive in terms of computing power and a method of indexing the spaces is required so that large numbers of containment relationships can be calculated cheaply. The invention is defined in the appended claims to which reference should now be made.